1. Field of the Invention
The present invention relates to a method of ultrasonic welding of different metals having different hardness such as steel and aluminum.
2. Description of the Related Art
The ultrasonic welding of different metals has been used because it is available at normal or low temperature.
However, when an extremely hard metal is welded to a soft metal by the ultrasonic welding, the bonding strength is not always ensured because the ultrasonic vibration cannot be transmitted to the soft metal.